The invention relates to a high-pressure dissolved-oxygen oxidizing treatment technique for treating wastewater, which comprises the following steps: adsorbent treatment, coagulative precipitation treatment, electrochemical and high-pressure dissolved-oxygen catalytic treatment and further coagulative precipitation treatment. The composite technique can effectively degrade various cyclic, high-molecular and other nondegradable organic matters, can effectively treat high-concentration organic wastewater, and greatly lowers the pollutant content in the wastewater. Meanwhile, the COD (chemical oxygen demand), total phosphorus and total nitrogen in the wastewater are effectively removed.